Here's what shows up at the bottom of the plugin's settings page after running a Test Report:
Warning: mysql_real_escape_string(): 9 is not a valid MySQL-Link resource in /home/.../wp-includes/wp-db.php on line 880That repeats 5 times.
Warning: mysql_error(): 9 is not a valid MySQL-Link resource in /home/.../wp-includes/wp-db.php on line 1220
In addition, does the Report return "Optimize Failed for table: ..." because the table is empty or because the table is non-WordPress? I have some empty, non-WP tables but also some non-empty, non-WP tables. The report says it failed to optimize any non-WP table, empty or not. It reports that such-and-such table "doesn't exist." However, they do all exist and are all fully functional.
This is a multisite install. I don't have the plugin network activated. It is optimizing all of the sites' tables by being enabled only via site 1.
I also installed the plugin on a non-multisite also with WP 3.8.1. It's working fine there and with the cron job working too.
Thanks in advance for your reply.